In situ characterization of a single fracture hydromechanical behavior from hydraulic pulse tests coupled to simultaneous pressure - normal displacement measurements

Abstract : Simultaneous measurements of fluid pressure and displacement normal to a fracture were performed for a series of seventy hydraulic pulse injection tests. The field tests were conducted in two horizontal boreholes spaced one meter vertically and intersecting a high-permeable vertical fault located within a 13 500 m3 fractured natural reservoir. Pulses tests were simulated with a coupled hydromechanical three-dimensional discrete model of the fractured rock. Field measurement and numerical modeling show that the hydraulic aperture and normal stiffness strongly vary along the fault plane. From the normal displacement versus fluid pressure relationship, modeling shows that the in situ intrinsic properties of the pressurized fault and the stiffness of the surrounding rock explain the fault hydromechanical behavior during the pulse pressure increase. During the pulse pressure decrease, the hydromechanical response of the pressurized fault is strongly influenced by the hydromechanical behavior of the other surrounding fractures of the network.